PWM inverter controller for starting and driving an AC motor

Abstract

A first memory stores first PWM control signal pattern data being calculated in advance according to the sine-triangle wave comparison modulation system in the frequency region below a predetermined frequency, for each of predetermined frequency intervals. A second memory stores second PWM control signal pattern data being calculated in advance according to the harmonic removal pattern modulation system in the frequency region above the predetermined frequency for each of predetermined frequency intervals. A frequency designating section supplies frequency designating data. A controller reads out, when receiving the frequency designating data, either the first or second PWM control signal pattern data in accordance with the frequency designating data, from the first or second memory. An inverter outputs a predetermined AC power in accordance with the read-out first or second PWM control signal pattern data. An AC motor is variably speed driven in accordance with the frequency designating data, when receiving the predetermined AC power from the inverter.

What is claimed is: 
     
       1. A PWM inverter controller for starting and driving an AC motor, comprising: PWM inverter means, responsive to a PWM control signal, for converting a DC voltage into an AC power output having a predetermined frequency;   an AC motor, responsive to said AC power output from said PWM inverter means, which is started when the predetermined frequency of said AC power output is in a starting range and which is driven at a variable-speed when the predetermined frequency of said AC power output is in a variable-speed driving range;   first storing means for storing first PWM control signal pattern data previously calculated based on a sine-triangle wave comparison modulation system over a frequency range corresponding to said starting range;   second storing means for storing second PWM control signal pattern data previously calculated based on a harmonic wave removal pattern modulation system, for predetermined frequency intervals, over a frequency range corresponding to said variable-speed driving range;   frequency designating means for selectively providing frequency designation data of the respective frequency ranges corresponding to said starting range and said variable-speed driving range;   first control means, responsive to said frequency designation data from said frequency designating means, for determining whether said frequency designation data is in said frequency range corresponding to said starting range or said frequency range corresponding to said variable-speed driving range, and for selecting said first storing means when said frequency range is determined to correspond to said starting range and for selecting said second storing means when said frequency range is determined to correspond to said variable-speed driving range, to thereby read out said first or second PWM control signal pattern data from said respective first or second storing means according to said frequency designation data; and   second control means, responsive to said first or said second PWM control signal pattern data read by said first control means, for converting said first or said second PWM control signal pattern into a corresponding PWM control signal and for supplying it as an input to said PWM inverter means.   
     
     
       2. The PWM inverter controller according to claim 1, wherein said AC motor is of an induction type and is used as a compressor motor for an air conditioner controlled by said PWM inverter means. 
     
     
       3. The PWM inverter controller according to claim 1, wherein said PWM inverter means includes an inverter main circuit having a plurality of transistors in a bridge configuration. 
     
     
       4. The PWM inverter controller according to claim 3, wherein said second control means includes a base drive circuit for driving said plurality of transistors in said inverter main circuit, in an ON/OFF fashion, in accordance with said PWM control signal.